Aerodynamic drag accounts for over 50% of a tractor trailer truck's total fuel consumption at highway speeds above 55 mph. A gap exits between the tractor and trailer which tends to trap air, creating a low-pressure wake behind the tractor, resulting in a net pressure difference and, therefore, creating drag. One solution has been to use fixed cab extenders to reduce the effect of unwanted drag. Ideally, the fixed cab extenders would extend across the entire gap between the tractor and trailer, which typically varies from 36 to 48 inches, to obtain maximum aerodynamic efficiency. However, if the fixed cab extenders were configured as described, as the tractor turned relative to the trailer, a front end of the trailer would impact and damage the fixed cab extenders.
Therefore, previously developed fixed cab extenders are positioned to have a large clearance space between a vertical trailing edge of the cab extender and the front end of the trailer. This clearance space is required to prevent the front surface of the trailer from impacting the fixed cab extenders during sharp, typically slow speed turns. Thus, there exists a need for a cab extender that may be selectively deployed within the clearance space to cover the space between the tractor and trailer at high speeds to improve fuel economy, and retracted at low speeds to allow the tractor trailer truck to maneuver.
Although fixed cab extenders have proven effective for decreasing the aerodynamic drag encountered by the tractor trailer truck, there are drawbacks to these improvements. For instance, a decrease in the aerodynamic drag of the truck causes a corresponding increase in the braking distance of the truck. This is especially true when the truck is operating at high altitudes where the air is less dense, and therefore provides a decreased stopping force, and where steep grades and brake fade are common. Therefore, there exists a need for a cab extender that may be selectively deployed into a decreased aerodynamic position to aid in stopping the vehicle during braking events.
U.S. Pat. No. 4,824,165 issued to Fry (hereinafter “Fry”) discloses one apparatus that attempts to fulfill the need for a cab extender that may be selectively deployed into a decreased aerodynamic position to aid in stopping a vehicle. Although somewhat effective, the apparatus of Fry is not without its problems. Referring to FIG. 3 of Fry, the braking actuators 44 are coupled to the wings 40 such that the braking actuators 44 bear substantially the full braking load exerted upon the wings 40. Thus, the braking actuators must be of substantial size and weight to withstand the braking load, leading to increased equipment costs and a decrease in fuel efficiency due to the increased weight of the braking actuators. Further, the wings 40 are not configurable into a stowed position to impede the wings 40 from being damaged during sharp turns. Therefore, the wings 40 must be of a reduced width such that when the tractor turns, the front end of the trailer does not impact the wings 40. Thus, as best seen in FIG. 4, a large clearance gap exists between the trailing edges of the wings 40 and the front end of the trailer 60. This large clearance gap significantly reduces the aerodynamic efficiency of the vehicle.